1. Field of the Invention
The present invention relate to a three-dimensional shape measurement technology.
2. Description of the Related Art
Three-dimensional shape measurement apparatuses that measure a three-dimensional shape of a target object have been widely used in various fields, such as component inspection in factories in the industrial field, and measurement of the shape of living organisms in the medical field. In particular, non-contact measurement methods are effective when a target object is liable to be deformed and damaged due to contact with an apparatus.
Various methods have been proposed as three-dimensional shape measurement methods. The types of three-dimensional shape measurement method are broadly classified into a passive type in which shape measurement is performed only by using a sensing apparatus but without using a projection apparatus, and an active type in which shape measurement is performed by using a sensing apparatus in combination with a projection apparatus. The active type has a higher robustness with respect to measurement objects than the passive type, and is capable of distance measurement with higher accuracy. Also, in the active type, even when there is little information on the surface texture of the measurement object, it is possible to perform shape measurement, gathering hints from projected patterns. Representative examples of the active type include measurement methods based on positions of projected patterns, measurement methods based on changes in phase information, and measurement methods based on information on defocusing of projected patterns.
Among these methods, a light-section method is known, which is a measurement suitable for dynamic scenes and in which a plurality of slit patterns are projected. In the light-section method in which a plurality of slit patterns are projected, all of the slit patterns to be projected have generally the same shape. Therefore, it is difficult to uniquely associate sensed slits with projected slits, unless for example a range of measurement distances is limited.
In this regard, Japanese Patent Laid-Open No. 2009-517634 discloses a method in which a plurality of slits that are encoded according to periodic changes in their widths are projected onto a measurement object. Codes are extracted from sensed slits and the extracted codes of the sensed slits are compared with codes of the projected slits. Then, according to the comparison result, the sensed slits are associated with the projected slits. Further, according to the association results, three-dimensional measurement is performed based on the principle of triangulation.
In the above-described configuration, however, when slits are adjacent to each other with a narrow gap, the adjacent slits may overlap with each other due to arrangement of codes arranged on the slits and blurring caused by an optical system of a projection apparatus, bringing about a problem of reducing a measurement accuracy.